Make Cortana play music for specific duration.

I just bought a microsoft invoke, and I've been trying to get it to play music for certain duration, say, for 30 minutes before I fall asleep. I tried telling Cortana to "play music for 30 min", "Stop music after 30 min", but doesn't seem to be able to have the command executed.

Is this something the Cortana can't do, or I just need to say something else?